Abstract

The coordination chemistry of four enantiopure tetradentate bis(iminoquinoline) ligands with nickel(II) salts is reported. The previously reported ligands CBQ, CPQ, BBQ, and BPQ result from the condensation of (1R,2R)-cyclohexyldiamine or (R)-BINAM with two equivalents of 2-formylbenzo[h]quinoline or 8-isopropyl-2-quinolinecarboxaldehyde {CBQ = (1R,2R)-cyclohexanediamine-N,N′-bis(benzo[h]quinoline-2-ylmethylene), CPQ = (1R,2R)-cyclohexanediamine-N,N′-bis[[(8-isopropyl)-2-quinolinyl]methylene], BBQ = [(R)-1,1′-binaphthalene]-2,2′-diamine-N,N′-bis(benzo[h]quinoline-2-ylmethylene), BPQ = [(R)-1,1′-binaphthalene]-2,2′-diamine-N,N′-bis[[(8-isopropyl)-2-quinolinyl]methylene]}. Reaction of NiI2 with the (1R,2R)-cyclohexyl ligands gives the mononuclear distorted trigonal-bipyramidal (TBP) complexes [Ni(N3-CBQ)I2] and [Ni(N3-CPQ)I2]. Incomplete iodide abstraction from [Ni(N3-CPQ)I2] with AgOTf leads to partial replacement of the iodide with hydroxide from adventitious water to give [Ni(N3-CPQ)I1.6(OH)0.4] (distorted TBP). The corresponding reaction with [Ni(N3-CBQ)I2] again fails to remove all of the iodide, resulting instead in conversion to the syn dinuclear [Ni2(CBQ)(μ-X)2I2] (X = Cl0.925I0.075) complex, where chloride abstraction from the solvent (CH2Cl2) has resulted in a mixed halide system and the metal centers are square-pyramidal. Reaction of Ni(OTf)2 with CBQ leads to the isolation of the octahedral cation [Ni(CMBQ)2]2+, with CMBQ [(1R,2R)-cyclohexanediamine-mono-N-(benzo[h]quinoline-2-ylmethylene)] being the partial hydrolysis product of CBQ. [Ni(CMBQ)2][OTf]2 crystallizes as a 1 : 1 mixture of P and M helical diastereomers. The coordination of NiI2 with the (R)-BINAM derived ligands yields the anti dinuclear P-helical complexes [Ni2(BBQ)(μ-I)2I2] and [Ni2(BPQ)(μ-I)2I2]: one nickel ion is coordinated in each bidentate iminoquinoline pocket and the geometry at the metal centers is distorted square-pyramidal. Characterisation by 1H NMR, UV-Vis, electronic circular dichroism (ECD) spectroscopy, combustion analysis, and HRMS is reported in addition to structural and halide abstraction studies.

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